Wireless communication systems continue to advance in sophistication, providing higher bandwidth, faster data rates, greater coverage, more efficient use of spectrum, and providing an ever-increasing breadth of services to subscribers. One technology that enhances bandwidth and data rates is the use of multiple transmit and receive antennas at one or both ends of the wireless channel, known as Multiple Input, Multiple Output (MIMO). Beginning with Release 10, up to eight layer MIMO transmission is supported in the 3GPP Long Term Evolution (LTE) standard.
The MIMO technique uses a commonly known notation (M×N) to represent MIMO configuration in terms number of transmit (M) and receive antennas (N). The common MIMO configurations used or currently discussed for various technologies are: (2×1), (1×2), (2×2), (4×2), (8×2) and (2×4), (4×4), (8×4). The configurations represented by (2×1) and (1×2) are special cases of MIMO.
A 4×4 MIMO system supports up to four layer spatial multiplexing. With four receiver antennas, an 8×4 MIMO system with four layer spatial multiplexing is capable of utilizing both beam forming and diversity gain in maximum level. These layers can be combined through dynamic beamforming and MIMO receiver processing to increase reliability and range. From a performance point of view, the use of four receiver antennas allows higher UE data rates in a wide range of scenarios and improved receiver sensitivity in general. Depending on the target SNR region, the transmission scheme used by the network, and the channel conditions, the peak throughput can be doubled compared to dual-layer multiplexing by virtue of additional diversity gain and/or multiplexing gain.
In prior art MIMO implementations, the network bases transmission parameters on static assumptions of UE antenna number, type, configuration, correlation, power imbalance, and the like. However, at least some of these UE antenna parameters may change over time and in dependence on channel conditions, operating band, available UE battery power, UE operating mode, physical orientation, and the like. When the use of static assumptions of UE antenna parameters by the network does not match actual UE antenna parameter values, system performance may not be optimal.
The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.